In the related art, a positron emission computed tomography (PET) apparatus has been known as a nuclear medicine imaging apparatus capable of performing functional diagnosis in body tissues of a subject.
Specifically, in a PET examination, a medical agent labeled by a positron emitting nuclide is introduced into a subject. In addition, the PET apparatus coincidentally counts a pair of gamma rays (annihilation gamma rays) of 511 keV emitted in the nearly opposite direction, when positrons emitted from the medical agent combine with electrons so as to be annihilated, using a detector composed of photon counting type detector modules arranged in a ring shape around the subject. In addition, the PET apparatus reconstructs a PET image by operating data of the coincidentally counted gamma rays (coincidence count information).
In recent years, a time-of-flight (TOF)-PET apparatus for precisely specifying the location where the gamma ray is emitted using the time difference between detection times of the annihilation gamma rays has been developed. Since the gamma ray propagates at a light velocity, the detection time difference required in the TOF-PET apparatus is about several hundreds of picoseconds. For this reason, in the TOF-PET apparatus, it is necessary to adjust the time information for determining the detection time of each detector module with high precision.
As a method of calibrating time information of each detector module, a technique using a point radiation source such as germanium-68 is typically used. In such a technique, the point radiation source is installed within a field of view (FOV) of the PET image, and the annihilation gamma rays generated from the point radiation source are detected by a pair of detector modules. In such a technique, the time information is calibrated using the detection time of a pair of detector modules detecting the annihilation gamma ray.
However, in the calibration method described above, a combination of two detector modules detecting the annihilation gamma rays is limited to a straight line shape passing through the point radiation source. Therefore, in the calibration technique described above, it is difficult to calibrate the time information of all detector modules.